This invention relates to automotive safety restraint systems and, in particular, to an active three-point seat belt system with a D-ring rotation restraint.
Numerous designs of passive and active automotive occupant restraint systems are known for enhancing occupant protection in the event of a vehicle crash. Passive systems such as inflatable restraints or air bags and automatically deployed seat belt systems are known. Active seat belt systems have been used for many decades and are manually deployed by the occupant. The conventional seat belt system uses three points of connection with the vehicle structure and incorporates a lap belt section for restraining the occupant's lower torso and a shoulder belt section for restraining the occupant's upper torso. The seat belt restrains movement of the occupant in the event of a vehicle impact or rollover event. In order to enhance the comfort and convenience provided by the seat belt system, retractors are normally used which permit the belt webbing to be extracted and retracted onto the retractor, allowing movement of the occupant while maintaining the belt in close contact with the occupant. An inertia sensitive actuator locks the retractors when an impact or rollover event is detected, preventing extraction of webbing.
A seat belt system may use a three-point restraint system having a fixed upper shoulder belt anchorage. More commonly, however, the shoulder portion of the seat belt webbing extends from a retractor mechanism secured to the interior of the vehicle, most often near the lower portion of the “B-pillar” with the lower end of the bolt attached to a fixed exchange or a second belt retractor. In such installations, the webbing undergoes a sharp bend and slides through and a narrow slotted opening in a “turning loop” or D-ring for extending down and across the occupant's torso to a tongue latch. The seat belt system is engaged when the occupant inserts the latch into a buckle. The D-ring may be attached to a height adjustment mechanism installed in the B-pillar in order to comfortably accommodate the size and height of the occupant. To facilitate extraction and retraction of the webbing as well as to maximize occupant comfort, the D-ring rotates about an axis defined by a fastener mounted to the height adjustment mechanism and the B-pillar.
When the vehicle rapidly decelerates, such as during a collision, the seat belt webbing may stretch, its edges may curl, and it may slide laterally forward and bunch up in the corner of the slotted opening in the D-ring, a condition known as bunching. As the webbing collects in the corner of the D-ring, the deceleration forces acting through the webbing on the D-ring tend to cause the leading edge of the D-ring to rotate downwards and backwards. As the webbing collects, or bunches, the tension forces exerted on the webbing are concentrated in the leading corner of the D-ring rather than distributed evenly across the entire length of the D-ring slotted opening. The bunching can also cause uneven loads on the webbing itself and can interfere with further controlled extraction of webbing desirable for load limiting operation, or belt restriction for belt tensioning as the slotted opening restricts movement of the bunched portion of the webbing.
It would be desirable to have a system which permitted the D-ring to rotate freely in order to accommodate extraction and retraction of webbing when the occupant attaches and detaches the seat belt, but which restricts backward rotation of the D-ring during a rapid deceleration to minimize bunching of the webbing.